Would a RS Products BM-1 Light Mount fit on a yugo OPAP rifle?

Yes and no. The standard BM-1 would need to be hogged out to fit. It's meant for the skinnier barrel the standard AKM pattern rifles use. RS is releasing a Yugo specific light mount just like the BM-1. I don't know its designation.

DBMG does make a Tri-Rail mount for oversized Yugo and Chinese barrels. Not a bad mount.  Same price. Bigger. Heavier. Not as refined according to people who have handled both. I'm waiting to get my hands on the me Yugo mount from RS to compare SxS.